Liquid crystal displays and VFD (vacuum fluorescent displays) have been put to use in display sections of mobile phones and displays mounted in vehicles and electronic appliances in recent years. Research and development efforts have been and being paid for organic ELs as promising choice for such displays. However, they have respective disadvantages. More specifically, (1) since liquid crystal does not emit light spontaneously and requires a back light when used in a display, the display is inevitably complex and it is difficult to design an ultimately thin display and (2) VFDs intrinsically provide a low display resolution and hence can display only simple images, whereas (3) Organic ELs have not been commercialized because of the problem of service life that has not hitherto been dissolved yet and (4) LEDs are accompanied by a problem that they require to be bundled by a large number to form a structure when they are used as illumination/display devices and hence are not very convenient.
Massive research and development efforts have been and are being paid for field electron emission type displays as alternative displays. Field electron emission type displays include FEDs (field emission displays) and SEDs (surface-conduction electron-emitter displays). It is expected that these devices and related systems will be putting on significance more and more in the future. As a matter of fact, intensive research efforts are being paid for the purpose of improving devices and systems of the type under consideration and developing new field electron emitting materials.
Field electron emitting materials are required to show a low field electron emission threshold, a high withstand voltage and a high current density. Materials recently attracting attention as field electron emitting materials include carbon nano-tubes. However, carbon nano-tubes require improvement of the electron emitting performance and the current density when designing an electron emitting material on the basis of this material. Efforts are being paid for patterning nano-tubes in order to grow thin film out of them and processing them to produce a profile adapted to electron emission.
However, the process of manufacturing carbon nano-tubes has not been perfectly established and the technological development for processing them is still under way. In short, it is very difficult to realize a field electron emission display on the basis of carbon nano-tubes. Additionally, the current density that can be achieved by way of a cumbersome process of treating carbon nano-tubes is in the order of mA/cm2 at most.
Carbon nano-tubes face a limit in terms of operating field intensity and problems such as degradation of material and exfoliation arise beyond the limit to make them undurable under hard operating conditions including a high voltage and a long operation time. While some reports say that displays using carbon nano-tubes are on the stage of experimental manufacture, the development of such displays is basically still in a difficult situation.
Field electron emission technologies are highly important. It will not be necessary to explain further that they influence not only specific technological fields but also the society at large and daily lives of ordinary people. Thus, more and more efforts will be paid for the development of field electron emission technologies. There is a strong demand for materials that can withstand a high field intensity and stably emit electrons with a high current density for a long period of time without degradation and damages.
The inventors of the present invention also have paid intensive research efforts in order to meet the demand and looked into boron nitride that is attracting attention as a heat-resistant and abrasion-resistant material. As a result of studies on electron emitting materials based on the compound, the inventors of the present invention came to find that boron nitride film that is prepared under certain conditions shows a surface profile that is remarkably good for emitting field electrons and withstands a high field intensity.
More specifically, the inventors of the present invention found that, in the process of producing and depositing boron nitride on a base (which may be flat plate-shaped, wiry, spherical or of some other shape) by way of a reaction from a gas phase, boron nitride of a certain bond type is formed as film on the base when ultraviolet rays are irradiated on and near the base with a high energy level and sp3 bond type boron nitride is produced with a pointed profile and grown in a self-organizing manner in the direction of irradiation of rays at appropriate intervals and that the obtained film easily emits electrons when an electric field is applied to it and can stably maintain its condition and performance without being degraded, damaged and exfoliated, maintaining an exceptionally large current density. The inventors have already applied for a patent for the achievement (see Patent Documents 1 and 2).
Patent Document 1: Jpn. Pat. Appln. Laid-Open Publication No. 2004-35301
Patent Document 2: Jpn. Pat. Application No. 2003-209489